Using Cyclic Prefix to Mitigate Carrier Frequency and Timing Asynchronism in Cooperative OFDM Transmissions

Abstract

While OFDM is a good modulation scheme for cooperative transmissions, the difficulty of synchronizing carrier frequencies of distributed transmitters presents one of the primary challenges. In this paper we show that cyclic prefix (CP) can be used not only to resolve the timing asynchronism, which is well-known, but also to mitigate the carrier frequency offsets (CFO) among the transmitters. Depending on the CP length, CFO can be mitigated or removed completely, which indicates an interesting trade-off between bandwidth efficiency and cooperation overhead.

On the Detection of Distributed STBC AF Cooperative OFDM Signal in the Presence of Multiple CFOs

“…The discrete multipath channel length are fixed to be L = 15 for all the channels. Each channel has 5 paths, and the path delay is defined as τ sd = [0, 2,5,9,13], τ sr = [0, 3,8,10,14] and τ rd = [0, 1,5,9,14]. The taps are modeled as independent circularly symmetric Gaussian random variables with zeromean (Rayleigh fading) and with exponential power delay profile…”

“…In cooperative networks, multiple CFOs due to the local oscillator frequency mismatch among distributed nodes is a serious problem, especially for cooperative OFDM systems. Multiple CFO mitigation using the redundancy of cyclic prefix (CP) is proposed in [10] for multiple relay systems without distributed coding. Interference mitigation methods of STBC decode-and-forward (DF) cooperative OFDM signals with multiple CFOs can be found in [11]- [13], and those of DSFC DF cooperative OFDM signal with multiple CFOs can be found in [14]- [16].…”

Multiple Frequency Offset Estimation and Mitigation for Cooperative OFDM System

“…Hu proposed a joint blind timing and CFOs estimation algorithm for MC-CDMA system based on oversampling [18] . In [16,17], X.H. Li proposed a technique to exploit the ISI free part of CP for multiple CFOs mitigation in the Cooperative OFDM system.…”